1. Field of the Invention
The present invention relates to an energization control method and an electromagnetic control system for an electromagnetic driving device including an armature, a pair of electromagnets disposed in an opposed relation to each other on opposite sides of the armature so as to be able to apply an electromagnetic attracting force to the armature, and a pair of return springs for biasing the armature toward the electromagnets. The present invention further relates to an electromagnetic driving device for an engine valve in an internal combustion engine in which an engine valve is operatively connected to an armature.
2. Description of the Prior Art
There is an electromagnetic driving device conventionally well-known, for example, from U.S. Pat. No. 5,222,714, which includes an armature, a pair of electromagnets disposed in an opposed relation to each other on opposite sides of the armature so as to be able to apply an electromagnetic attracting force to the armature, and a pair of return springs for biasing the armature toward the electromagnets, respectively. There is also an electromagnetic driving device conventionally known, for example, from Japanese Patent Application Laid-open No.44716/82, which includes an armature, a pair of electromagnets disposed in an opposed relation to each other on opposite sides of the armature so as to be able to exhibit an electromagnetic force for attracting the armature, a pair of return springs for biasing the armature toward the electromagnets, respectively, and an equilibrium position changing means for changing the equilibrium neutral position of the armature maintained by both the return springs in deexcited states of the electromagnets between a first position which is substantially halfway between both the electromagnets and a second position in which the armature is in proximity to one of the electromagnets. Further, there is an electromagnetic driving device for an engine valve in an internal combustion engine known, for example, from Japanese Patent Application Laid-open No.213913/84, which includes an armature operatively connected to the engine valve, a valve-closing electromagnet for exhibiting an electromagnetic force for attracting the armature to close the engine valve, a valve-opening electromagnet for exhibiting an electromagnetic force for attracting the armature to open the engine valve, a valve-closing return spring for biasing the armature in a direction to close the engine valve, and a valve-opening return spring for biasing the armature in a direction to open the engine valve.
In the electromagnetic driving device disclosed in U.S. Pat. No. 5,222,714, the energization of the electromagnets is controlled with a given energization amount. However, the attracting electromagnetic forces exhibited by the electromagnets, if the electromagnets are energized with the same energization amount, are decreased in accordance with an increase in temperature, and therefore, with an increase in temperature, the attracting and maintaining of the armature by the electromagnets are liable to fail. When the inertial force of the armature is increased with an increase in the number of operations per unit of time, the attracting and maintaining of the armature by the electromagnets are liable to fail, if they exhibit the same attracting electromagnetic force.
In the electromagnetic driving device disclosed in Japanese Patent Application Laid-open No.44716/82, the armature is connected to an engine valve as an intake valve or an exhaust valve, and the equilibrium position changing means is provided to forcibly move the engine valve to a closed position at the start of an engine. During operation of the engine, the equilibrium position changing means shifts the equilibrium neutral position of the armature to a position which is substantially halfway between both the electromagnets. However, if the attraction of the armature by one of the electromagnets which attracts the armature in a valve closing direction becomes incomplete during operation of the engine, the engine valve starts an opening lifting before being closed under the action of the spring forces of return springs, and starts to be closed before reaching a maximum lifted position, and the armature starts a free vibration without being maintained on any of electromagnets. Such a free vibration is likewise produced even when the movement of the armature toward the electromagnet which exhibits the attracting electromagnetic force in a valve-opening direction becomes incomplete. If the vibration is produced in this manner, there is a possibility that interference of the piston and engine valve with each other may be produced depending upon the position of the piston, and interference of the intake and exhaust valves with each other is also produced and as a result, a different sound may be generated and a defective deformation and operation of the piston and engine valve may be produced.
Further, in the electromagnetic driving device for the engine valve in the internal combustion engine disclosed in Japanese Patent Application Laid-open No.213913/84, an operating force for operating the engine valve in a closing direction and an operating force for operating the engine valve in an opening direction are set equally. However, when the engine valve fails to operate in the opening direction, only a reduction in engine output is produced, and it is possible to continue the operation of the engine, and there is less influence on the operation of the engine. On the other hand, when the engine valve fails to operate in the closing direction, there is a possibility of a reduction in compression ratio, a misfire and a back fire may be produced, resulting in stopping of the engine. Therefore, it is necessary to reliably operate the engine valve in the closing direction. For this purpose, it is necessary to equally increase both of the operating force in the valve-closing direction and the operating force in the valve-opening direction. As a result, in opening the engine valve, it is operated in the opening direction with an operating force larger than necessary, which wastefully causes electric power to be consumed.